1. Field of the Invention
The present invention relates to a solid-state imaging device, a method of producing the solid-state imaging device, and a piece of electronic equipment.
2. Description of the Related Art
A piece of electronic equipment such as a digital video camera, digital camera or the like includes a solid-state imaging device. For example, as the solid-state imaging device, a CMOS (Complementary Metal Oxide Semiconductor) type image sensor and a CCD (Charge Coupled Device) type image sensor are included.
In the solid-state imaging device, a capturing area in which a plurality of pixels is arranged in a matrix shape is provided on a surface of a semiconductor substrate. Photoelectric transformation portions are provided on each of the plurality of pixels. The photoelectric transformation portions are, for example, photodiodes, and create a signal electric charge by receiving light, which is incident via an externally attached optical system, at a light sensing surface to perform a photoelectric transformation.
In the solid-state imaging device, a micro lens is disposed at an upper part of the light sensing surface of the photoelectric transformation portion, so that the incident light is concentrated to the light sensing surface by the micro lens.
Since the sensitivity difference is generated between a center portion of the capturing area and the surrounding portion thereof in the solid-state imaging device, the image quality of the captured image declines.
Specifically, in the center portion of the capturing area, the angle of the main ray, which is incident via the externally attached optical system, is nearly perpendicular to the light sensing surface in the center portion of the capturing area, whereas the angle of the incident main ray slopes in the surrounding portion of the capturing area. For this reason, the center portion of the captured image becomes a light image and the surrounding portion becomes a dark image, whereby the image quality of the captured image declines. That is, a so-called shading phenomenon is generated, whereby the image quality declines.
In addition, in a case where the color image is captured, when the incident light is incident obliquely with respect to the light sensing surface, the incident light is not incident to just below the light sensing surface but is naturally incident to other light sensing surface that receive the colored light of other color. For this reason, a so-called “mixed color” is generated, and the deviation of shade is generated in the captured color image, whereby the image quality declines.
Particularly, in electronic equipment used for a miniaturized mobile application such as a mobile phone with a camera, since the distance between the externally attached optical system and the light sensing surface of the image sensor is short, the occurrence of the disadvantage as above may become an issue.
In order to improve the disadvantage, the correction of the arrangement of the micro lens or the like called “pupil correction” is carried out. For example, it is carried out to provide the micro lens so that the position of the micro lens disposed around the capturing area is shifted to the center side of the capturing area with respect to the light sensing surface (e.g., Japanese Patent No. 2600250 and Japanese Unexamined Patent Application Publication No. 2003-273342).
As the above-mentioned micro lens, a refraction type lens, which uses the refraction of the surface, such as a spherical lens and a Fresnel lens is used.
In addition, as the above-mentioned micro lens, lenses, which do not use the refraction of the surface, such as a refractive index profile type lens or a diffractive lens are used. Herein, a digital lens having a rectangular sectional shape is provided as the micro lens (e.g., see Japanese Unexamined Patent Application Publication Nos. 2005-203526, 2006-344752, 2006-351972, 2008-10773, 2008-16722, and 2009- 15315).
For example, the micro lens includes a plurality of layers with different refractive indexes, and the plurality of layers is alternately arranged in a transverse direction perpendicular to an optical axis of the micro lens. Furthermore, the micro lens is configured by providing the plurality of layers with different refractive indexes in a depth direction along the optical axis of the micro lens. The micro lens is a concentration element (SWLL: Subwave Length Lens) which has a periodic structure of a wavelength order or a sub wavelength area smaller than that, and a high concentration efficiency can be realized by a thin film.